Toxins and Radionuclides Coupled to IGF-1 Receptor Ligands for Treatment of Cancer

ABSTRACT

The invention provides an insulin-like growth factor-1 (IGF-1) receptor ligand carrying a therapeutic radionuclide for treatment of cancer is provided. A method of treating cancer using the IGF-1 receptor ligand carrying a therapeutic radionuclide is also provided. An anti-cancer therapeutic agent containing an IGF-1 receptor ligand linked to a toxin is also provided, as are methods of using the toxin conjugates for treatment of cancer.

This application is a continuation-in-part application claiming priorityunder 35 U.S.C. §120 from international patent application no.PCT/US05,037739, filed Oct. 21, 2005, which claims priority from U.S.provisional patent application Ser. No. 60/620,794, filed Oct. 21, 2004.

BACKGROUND

Currently 1.3 million people are diagnosed with cancer each year in theUnited States alone, and over 500,000 die. One method emerging as a newtype of treatment for cancer is a type of radiation therapy using anantibody coupled to a therapeutic radionuclide, where the antibodyrecognizes a target that is specific for a particular type of cancer orfound predominantly on cancerous cells. Two examples are currentlyapproved for treatment in the United States: ibitrumomab tiuxetan(ZEVALIN®) and tositumomab (BEXAR®). Ibitrumomab tiuxetan recognizes theCD20 antigen, which is found on normal and malignant B cells. Theantibody is coupled to a therapeutic Yttrium-90 radionuclide by atiuxetan chelator moiety. Tositumomab also recognizes the CD20 antigen,but it is labelled with a I-131 radionuclide. Both are used to treatB-cell non-Hodgkin's lymphoma.

Anti-cancer agents involving toxins, such as diphtheria toxin orPseudomonas exotoxin, coupled to antibodies that recognize targets foundon cancerous cells have also been studied, although no agents of thistype are currently approved in the United States.

New agents for treating cancer are needed. Preferably the agents wouldbe targeted to cancer cells and largely spare healthy cells.

SUMMARY

The invention provides new anti-cancer therapeutic agents involvingligands to the insulin-like growth factor-1 (IGF-1) receptor, such asIGF-1 itself, coupled to a therapeutic radionuclide or to a cellulartoxin such as diphtheria toxin or Pseudomonas exotoxin.

In previous work, toxins and radionuclides have been coupled toantibodies to deliver them to antigens found specifically on cancercells. One drawback to the use of antibodies is that antibodies arelarge molecules that often generate an immune response andhypersensitivity response in patients to whom they are administered.This can interfere with their use therapeutically. The size ofantibodies also means they may not penetrate solid tumors efficiently.Antibodies also are not typically internalized by the cells to whichthey bind. They simply sit on the cell surface. Withradionuclide-labelled antibodies, it would be somewhat preferable if theradionuclide were internalized to the target cell and thus were closerto the nucleic acids of the cell, which are the therapeutic target ofthe radioactivity than it is on the surface of the cell. Withtoxin-conjugated antibodies, it is a larger problem if the antibody andtoxin are not internalized into the target cancer cell, since toxinstypically must be internalized by the cell in order to kill the cell.

The defining feature of cancer is that cancerous cells divide withoutappropriate control. Radiation is used in anti-cancer therapy becauseradiation is more toxic to actively dividing cells than to resting cellsthat are not dividing. But cancer cells are not always dividing. Theeffectiveness of radiation therapy could be increased if the cells couldbe induced to divide at or around the time they are exposed toradiation.

The IGF-1 receptor is significantly overexpressed in most tumors fromalmost all types of cancer. IGF-1 is a peptide of 70 amino acid residueshaving 40% identity with proinsulin. (Daughaday, W. H., et al., 1989,Endocrine Revs. 10:68.) IGF-1 is secreted by the liver into thecirculatory system and stimulates growth of many cell types. IGF-1 isalso produced by many cell types throughout the body, including manycancers, for autocrine and paracrine effects. IGF-1 production isstimulated by growth hormone. (Stewart, C. H., e t al., 1996, Physiol.Revs. 76:1005; Yakar, S., et al., 2002, Endocrine 19:239.) IGF-1receptors were found to be 43 times more numerous on malignant breastcancer tissue than benign breast tissue (Jammes, H. et al. Br. J. Cancer66:248-253).

IGF-1's biological role is to stimulate cell division. This issignificant since radiation is more toxic to dividing cells thannon-dividing cells. Thus, a radioactively labelled IGF-1 receptoragonist not only will be targeted with a high degree of specificity tocancer cells, but it may also cause the cells to divide as they arebeing irradiated, thus sensitizing them to the radiation.

Furthermore, upon binding to its receptor, IGF-1 is internalized to thecell by receptor-mediated endocytosis. This brings a radionuclideattached to IGF-1 or to another IGF-1 receptor ligand into the cell andcloser to the target nucleic acids. This factor is more important fortoxin-IGF-1 receptor ligand conjugates, since it brings the toxin intothe cell, and most toxins must penetrate the cell in order to exerttheir toxicity.

Accordingly, one embodiment of the invention provides an insulin-likegrowth factor (IGF-1) receptor ligand carrying a therapeuticradionuclide.

Another embodiment of the invention provides an anti-cancer therapeuticagent comprising: an IGF-1 receptor ligand linked to a toxin.

Another embodiment of the invention provides a method of treating cancerin a mammal involving administering to the mammal a therapeuticallyeffective amount of an IGF-1 receptor ligand carrying a therapeuticradionuclide.

Another embodiment of the invention provides a method of treating cancerin a mammal involving administering to the mammal a therapeuticallyeffective amount of a therapeutic agent containing an IGF-1 receptorligand linked to a toxin.

Another embodiment of the invention provides a method of inhibitinggrowth of cancer cells involving contacting the cancer cells with anIGF-1 receptor ligand carrying a therapeutic radionuclide.

Another embodiment of the invention provides a method of inhibitinggrowth of cancer cells involving contacting the cancer cells with atherapeutic agent containing an insulin-like growth factor-1 (IGF-1)receptor ligand linked to a toxin.

Another embodiment of the invention provides a method of screening acompound for anti-cancer activity involving contacting cancer cells witha compound comprising an IGF-1 receptor ligand carrying a therapeuticradionuclide.

Another embodiment of the invention provides a method of screening acompound for anti-cancer activity involving contacting cancer cells witha compound comprising an IGF-1 receptor ligand linked to a toxin.

DETAILED DESCRIPTION Definitions

As used herein, the term “toxin” refers to a molecule or moiety that isgenerally lethal to all cells. This contrasts with traditionalanti-cancer chemotherapy agents, which are selectively lethal todividing cells and less lethal to non-dividing cells. Anti-cancerchemotherapy agents

that are selectively lethal to dividing cells and can be administeredsytemically to treat cancer in mammals are excluded from the term“toxin” as used herein.

As used herein, the term “therapeutic radionuclide” refers to an atomthat emits a form of radiation that is therapeutically useful to killcancer cells.

As used herein, the term “containing” is open-ended, allowing theinclusion of other unnamed elements, and has the same meaning as“comprising.”

Description

One embodiment of the invention provides an IGF-1 receptor ligandcarrying a therapeutic radionuclide. The radionuclide can be directlycoupled to the ligand in some embodiments—for example by iodination oftyrosine or histidine residues on a protein ligand with I-131.

In other embodiments, the radionuclide is coupled to the ligand by alinker moiety. The linker moiety may include a chelator for holding theradionuclide. An example of a chelator is tiuxetan[N-[2-bis(carboxymethyl)amino]-(p-isothiocyanateophenyl)-propyl]-[N-[2-bis(carboxymethyl)amino]-2-(methyl)-ethyl]glycine].Another example of a ligand for coupling isdiethelyenetriaminepentaacetic acid (DTPA). Methods of radiolabellingIGF-1 ligands directly or with chelator linkers are described in greaterdetail in Example 1.

Examples of suitable radionuclides are Iodine-131, Yttrium-90,Indium-111, Rhenium-186, and Lutetium-177. These are all beta or gammaemitters with short half lives. With IGF-1 receptor ligands that areinternalized into the cell, alpha emitters may also be therapeuticallyeffective radionuclides. Alpha particles are absorbed in such shortdistances that they are ordinarily not therapeutically useful whenemitted from the surface of a cancer cell or the outer surface of atumor. But many ligands to IGF-1 receptor will be internalized byreceptor-mediated endocytosis. This will bring the radionuclide into thenucleus of the cell, in direct contact with the DNA target. Thus, inthat case an alpha emitting radioisotope may be useful.

The IGF-1 receptor ligand carrying a therapeutic radionuclide can be anIGF-1 receptor agonist. An agonist will stimulate cell division, andsince radiation is more lethal for dividing cells than non-dividingcells, this will sensitize the cancerous cells to killing by theradiation. An example of a suitable IGF-1 receptor ligand that is anagonist is IGF-1 itself. The sequence of human IGF-1 is presented as SEQID NO:1.

Other examples of IGF receptor agonists suitable for use in theinvention include variants of IGF-1 that activate the receptor but havereduced affinity for the soluble IGF-1 binding proteins. Some examplesare disclosed in U.S. Pat. No. 4,876,242. IGF-1 binding proteins arenatural serum proteins that bind to IGF-1, holding it in circulation andextending its biological half-life. It may be advantageous forradiolabelled and toxin-linked IGF-1 receptor ligands of this inventionto have reduced binding to the IGF-1 binding proteins, because thatreduced binding would accelerate the release of the agent to bind to theIGF-1 receptors. A particularly important variant of IGF-1 that binds tothe IGF receptor but not to the soluble IGF binding proteins is thevariant in which the first 16 residues of IGF-1 are replaced by thefirst 17 residues of the B-chain of insulin (U.S. Pat. No. 4,876,242)(SEQ ID NO:2). Another preferred IGF-1 protein variant with reducedbinding affinity for the soluble IGF-1 binding proteins is R3-IGF-1 (SEQID NO:9), in which the Glu at position 3 of SEQ ID NO:1 is replaced withArg. Another preferred variant IGF-1 protein is SEQ ID NO:10 (Francis,G. L. et al., 1992, J. Mol. Endocrinol. 8:213-223; Tomas, F. M. et al.,1993, J. Endocrinol. 137:413-421).

The variant IGF-1 protein, preferably includes a polypeptide segment atleast 80%, more preferably at least 90% identical to native IGF-1 (SEQID NO:1).

In another particular embodiment, the IGF-1 receptor agonist is IGF-2(SEQ ID NO:8).

In particular embodiments of the invention, the toxin conjugates andradiolabelled agents include a variant IGF-1 protein that has reducedbinding affinity for the soluble IGF-1 binding proteins. In particularembodiments, the variant has greater than 100-fold lower, morepreferably greater than 1000-fold lower, binding affinity for thesoluble IGF-1 binding proteins than does native IGF-1. Binding affinityfor the soluble IGF-1 binding proteins can be assayed as described inBayne, M. L. et al., 1988, J. Biol. Chem. 263:6233-6239; and Bayne, M.L. et al., 1987, Proc. Natl. Acad. Sci. USA 84:2638-2642. The techniqueinvolves measuring the variant IGF-1's inhibition constant forinhibiting ¹²⁵I-IGF-1 binding to the acid-stable protein fraction ofhuman serum.

In particular embodiments of the invention, the IGF-1 receptor ligandthat is radiolabelled or part of a toxin conjugate has a K_(D) for theIGF-1 receptor of less than less than 10 μM, less than 1 μM, less than100 nM, less than 50 nM, less than 20 nM, less than 10 nM, less than 5nM, less than 2 nM, or less than 1 nM. Preferably, the ligands have aK_(D) for the IGF-1 receptor of less than about 50 nM, more preferablyless than about 20 nM. Binding affinity for the IGF-1 receptor can bedetermined as described, for instance, in Bayne, M. L. et al., 1988, J.Biol. Chem. 263:6233-6239; and Bayne, M. L. et al., 1987, Proc. Natl.Acad. Sci. USA 84:2638-2642, by measuring competition with radiolabelledIGF-1 for binding to placental membranes.

In some embodiments, the IGF-1 receptor ligand is an IGF-1 receptorantagonist. Some antagonist peptides are disclosed in U.S. publishedpatent application No. 2004/0023887, including the peptideSFSCLESLVNGPAEKSRGQWDGCRKK (SEQ ID NO:3).

In particular embodiments, the IGF-1 receptor ligand has a greateraffinity for the IGF-1 receptor than for the insulin receptor. Inparticular embodiments, the IGF-1 receptor ligand is not insulin. Inparticular embodiments, the IGF-1 receptor ligand has a higher affinityfor the IGF-1 receptor than for the insulin receptor.

In particular embodiments, the IGF-1 receptor ligand is not an antibodyor an antibody fragment. In other embodiments, the IGF-1 receptor ligandis an antibody or antibody fragment.

In particular embodiments, the IGF-1 receptor ligand is a polypeptide offewer than 200 amino acid residues or fewer than 100 amino acidresidues.

One embodiment of the invention is an anti-cancer therapeutic agentcontaining an IGF-1 receptor ligand linked to a toxin.

In particular embodiments of the toxin conjugates, the IGF-1 receptorligand is an IGF-1 receptor agonist. For instance, it can be IGF-1 orone of the variant IGF-1s of U.S. Pat. No. 4,876,242 that has reducedbinding to the soluble IGF-1 binding proteins.

In some embodiments, the IGF-1 receptor ligand is an IGF-1 receptorantagonist. Some antagonist peptides are disclosed in U.S. publishedpatent application No. 2004/0023887, including the peptideSFSCLESLVNGPAEKSRGQWDGCRKK (SEQ ID NO:3).

In particular embodiments of the toxin conjugates, the IGF-1 receptorligand has a greater affinity for the IGF-1 receptor than for theinsulin receptor. In particular embodiments, the IGF-1 receptor ligandis not insulin. In particular embodiments, the IGF-1 receptor ligand hasa higher affinity for the IGF-1 receptor than for the insulin receptor.

In particular embodiments of the toxin conjugates, the IGF-1 receptorligand is not an antibody or an antibody fragment. In other embodiments,the IGF-1 receptor ligand is an antibody or antibody fragment.

In particular embodiments of the toxin conjugates, the IGF-1 receptorligand is a polypeptide of fewer than 200 amino acid residues or fewerthan 100 amino acid residues.

In particular embodiments, the toxin is diphtheria toxin, Pseudomonasexotoxin, Clostridium perfringens enterotoxin, ricin, or a toxicfragment thereof.

In particular embodiments, the toxin portion of the IGF-1 receptorligand-toxin conjugate is a toxic fragment of a naturally occurringtoxin. Most bacterial toxins, such as diphtheria toxin, Pseudomonasexotoxin, and Clostridium perfringens enterotoxin, include areceptor-binding moiety that targets the toxin to a particularcell-surface receptor, and a moiety that is responsible for the toxicityof the toxin protein. For instance, Clostridium perfringens enterotoxinbinds to claudin-3 and claudin-4 on the cell surface. Clostridiumperfringens enterotoxin (CPE) is a protein of 319 amino acid residues(SEQ ID NO:4). A peptide consisting of residues 290-319 of Clostridiumperfringens enterotoxin binds to claudin-3 and claudin-4 but is nottoxic (Hanna, P. C., et al., 1991, J. Biol. Chem. 266:11037-43).Approximately residues 45-116 of CPE are responsible for cytolysis ofcells through forming large complexes in the cell membrane (Kokai-Kun,J. F. et al., 1996, Infect. Immun. 64:1020-25; Kokai-Kun, J. F. et al.,1997, Clin. Infect. Dis. 25 (Suppl. 2):S165-5167; Kokai-Kun, J. F. etal., Infect. Immun. 65:1014-1022; Kokai-Kun, J. F. et al., 1999, Infect.Immun. 67:5634-5641; Hanna, P. C., et al., 1991, J. Biol. Chem.266:11037-43). Deletion of just residues 315-319 is enough to abolishbinding to the receptors (Kokai-Kun, J. F. et al., 1999, Infect. Immun.67:5634-5641). Thus, in some embodiments of the present toxinconjugates, the toxin moiety of the conjugates is a fragment of CPEcontaining residues 45-116 of SEQ ID NO:4, but lacking residues 315-319of SEQ ID NO:4. For instance, the toxin may be residues 1-314, 1-289,1-116, 45-314, 45-289, 45-116, or 45-223 of SEQ ID NO:4.

In other embodiments, the toxin is diphtheria toxin or a toxic fragmentthereof. Diphtheria toxin is a protein of 535 amino acid residues (SEQID NO:5). It contains three domains. Residues 1-193 are the catalyticdomain, having the ADP-ribosyl transferase activity that is responsiblefor inactivating elongation factor-2 in cells to kill them (Choe, S. etal., 1992, Nature 357:216-222). Approximately residues 203-378 areresponsible for translocation of the toxin across the cell membrane(id). And approximately residues 386-535 are responsible for binding tothe receptor (id). Fusions of interleukin-2 to residues 1-389 ofdiphtheria toxin have been found to be more cytotoxic against cellshaving interleukin-2 receptors than fusions to longer fragments ofdiphtheria toxin (Williams, D. P. et al., 1990, J. Biol. Chem.265:11885-89); Kiyokawa, T. et al., 1991, Protein Engineering4:463-468). Thus, in a particular embodiment, the toxin portion of thepresent conjugates is residues 1-389 of SEQ ID NO:5.

In one embodiment, the toxin-IGF-1 receptor ligand conjugate is orcomprises SEQ ID NO:6, which is residues 1-389 of diphtheria toxincoupled to the variant IGF-1 SEQ ID NO:2 that does not bind to thesoluble IGF-binding proteins. The diphtheria toxin portion (DPT) andIGF-1 portion of the conjugate in SEQ ID NO:6 are separated by a His-Alalinker. In another embodiment, the toxin-IGF-1 receptor ligand conjugateis a DPT-IGF-1 fusion protein that is or comprises SEQ ID NO:12.

In another embodiment, the toxin-IGF-1 receptor ligand conjugate is orcomprises SEQ ID NO:7, which is residues 45-289 of Clostridiumperfingens enterotoxin (CPE) coupled to SEQ ID NO:2. The CPE portion andIGF-1 portion of the conjugate in SEQ ID NO:7 are separated by a His-Alalinker.

In another embodiment, the toxin portion toxin-IGF-1 receptor ligandconjugate is or comprises residues 45-116, 45-223, or 45-310 of SEQ IDNO:4.

In another embodiment, the toxin-IGF-1 receptor ligand conjugate is aCPE-IGF-1 fusion protein that is or comprises SEQ ID NO:11 or residues14-275 of SEQ ID NO:11. Residues 14-275 of SEQ ID NO:11 are residues14-223 of CPE at the N-terminus followed by at its C-terminus an IGF-1variant (SEQ ID NO:10) with reduced binding to the soluble IGF-1 bindingproteins.

Toxins can be chemically conjugated to proteinaceous IGF-1 receptorligands by methods disclosed in U.S. provisional patent application Ser.No. 60/513,048 and international patent application WO2005/041865, whichare incorporated by reference.

Where the toxins and IGF-1 receptor ligands are both proteins orpeptides, the conjugates are preferably fusion proteins, expressed byrecombinant DNA methods, of the toxins and the IGF-1 receptor ligands.

In particular embodiments of the toxin conjugates, the toxin is acalicheamicin or a derivative thereof (Merck Index 13^(th) edition,#1722). Specifically it may be calicheamicin γ₁ ^(I) or a derivativethereof. Derivatization of the calicheamicins typically occurs on thetrisulfide (Hamann, P. R. et al., 2005, Bioconjugate Chem. 16:346-353;Hinman, L. M. et al., pp. 87-106 in Enediyne Antibiotics as AntitumorAgents, D. B. Borders, T. W. Doyle, eds., Marcel Dekker Inc. New York,1995). The calicheamicins are sometimes considered considered to beconventional anti-cancer chemotherapy agents in contradistinction totoxins. But they are treated as “toxins” herein because whenadministered systemically without conjugation to a targeting agent, ator below the doses that in the short term are most effective againsttumors in an animal model, they exhibit almost 100% delayed lethality tothe animals (Dun, F. E. et al. pp. 127-136 in Enediyne Antibiotics asAntitumor Agents, D. B. Borders, T. W. Doyle, eds., Marcel Dekker Inc.New York, 1995).

Preferably, an IGF-1 receptor ligand that is a protein (e.g., SEQ IDNO:1 or SEQ ID NO:2) is conjugated through one or more of its lysineresidues to N-acetyl-calicheamicin γ₁ ^(I). N-acetyl-calicheamicin γ₁^(I) can be made by acetylating calicheamicin γ₁ ^(I) in methanol in anexcess of acetic anhydride. NAc-gamma calicheamicin dimethyl acidO-succinimidyl ester (compound 6 in Hamann, P. R. et al., 2005,Bioconjugate Chem. 16:346-353) is prepared as described in Hamann, P. R.et al., 2002, Bioconjugate Chem. 13:40-46. This activated succinimidylester reacts with amine groups on proteins to form an amide bondconjugate between the IGF-1 receptor ligand and N-acetyl-calicheamicinγ₁ ^(I).

One embodiment of the invention is a method of treating cancer in amammal involving administering to the mammal a therapeutically effectiveamount of an IGF-1 receptor ligand carrying a therapeutic radionuclide.In particular embodiments, the cancer is non-small cell lung cancer,prostate cancer, colorectal cancer, breast cancer, pancreatic cancer,Hodgkin's lymphoma, non-Hodgkin's lymphoma, leukemia, liver cancer,stomach cancer, ovarian cancer, uterine cancer, testicular cancer, braincancer, or melanoma.

One embodiment of the invention is a method of treating cancer in amammal involving administering to the mammal a therapeutically effectiveamount of a therapeutic agent containing an insulin-like growth factor-1(IGF-1) receptor ligand linked to a toxin. In particular embodiments,the cancer is non-small cell lung cancer, prostate cancer, colorectalcancer, breast cancer, pancreatic cancer, Hodgkin's lymphoma,non-Hodgkin's lymphoma, leukemia, liver cancer, stomach cancer, ovariancancer, uterine cancer, testicular cancer, brain cancer, or melanoma.

One embodiment of the invention is a method of inhibiting growth ofcancer cells involving contacting the cancer cells with an IGF-1receptor ligand carrying a therapeutic radionuclide. The contacting canbe in vivo or in vitro. In particular embodiments, the IGF-1 receptorligand carrying the therapeutic radionuclide kills the cancer cells.

Another embodiment of the invention is a method of inhibiting growth ofcancer cells involving contacting the cancer cells with a therapeuticagent containing an IGF-1 receptor ligand linked to a toxin. Thecontacting can be in vitro or in vivo. In particular embodiments, thecancer cells are killed.

Another embodiment of the invention is a method of screening a compoundfor anti-cancer activity involving contacting cancer cells with acompound comprising an IGF-1 receptor ligand carrying a therapeuticradionuclide. The method involves monitoring the growth or killing ofthe cancer cells. The contacting can be in vitro or in vivo.

Another embodiment of the invention involves screening a compound foranti-cancer activity involving contacting cancer cells with a compoundcomprising an IGF-1 receptor ligand linked to a toxin. The methodinvolves monitoring the growth or killing of the cancer cells. Thecontacting can be in vitro or in vivo.

The invention will now be illustrated by the following non-limitingexamples.

Example 1 Treatment of a Mouse Breast Cancer Model with ¹³¹I-IGF-1 and⁹⁰Y-IGF-1 Materials and Methods

IGF is radioiodinated with 1-131 (Amersham Biosciences) by use of theIODO-GEN method (1,3,4,6-tetrachloro-3α,6α-diphenylglycoluril; PierceBiotechnology, Inc). Briefly, IGF-1 is incubated at room temperature in85 μl PBS (0.1 M, pH 7.4) in a glass vial coated with 50-100 μg ofIODO-GEN. After 10 min, the reaction is stopped by the addition of 100μl of a saturated tyrosine solution. The reaction mixture then isseparated on a PD-10 column (Amersham Biosciences), eluting with PBS and0.5% bovine serum albumin. The specific activity is approximately 80kBq/μg (Koppe, M. J. et al. 2004. J. Nucl. Med. 45:1224-1232).

To label with Y-90, IGF-1 is conjugated withisothiocyanato-benzyl-diethylenetriaminepentaacetic acid (ITC-DTPA,Macrocyclics, Inc.). ITC-DTPA is conjugated to IGF-1 in NaHCO₃ buffer(0.1 M, pH 8.2) by use of a 100-fold molar excess of ITC-DTPA asdescribed by Ruegg et al. (Ruegg, C. L. et al., 1990, Cancer Res.50:4221-26) for 1 hour at room temperature. The DTPA-IGF-1 conjugate ispurified by dialysis against ammonium acetate buffer (0.1M, pH 5.0). Thenumber of DTPA ligands per IGF-1 molecule can be determined by themethod of Hnatowich, D. J. et al. 1983, J. Immunol. Methods 65:147-157.Up to three ligands may be conjugated per IGF-1. The purified DTPA-IGF-1conjugate (0.8 mg/ml) is incubated with Y-90 (Perkin-Elmer Corp.) inammonium acetate buffer (0.1 M, pH 5.4) at room temperature for 20minutes. The specific activity is approximately 370 kBq/μg (Koppe, M. J.et al. 2004. J. Nucl. Med. 45:1224-1232).

The radiolabelled preparations are purified by gel filtration on a PD-10column (Amersham), eluting with PBS with 0.5% bovine serum albumin. Theamount of free radioisotope is determined by thin-layer chromatographywith silica gel strips and citrate buffer (0.1 M, pH 6.0) as the mobilephase. Less than 5% of the label should be unconjugated to IGF-1.

The maximal tolerated dose of unlabelled IGF-1, ¹³¹I-IGF-1, and⁹⁰Y-IGF-1 is determined in six-week old female nude mice (nu/nu, SpragueDawley, Madison, Wis.).

MCF-7 is a human breast cancer cell line that is responsive to IGF-1(Dupont, J., et al., 2003, J. Biol. Chem. 278:37256). MCF-7 cells arecultured in F12/DME medium supplemented with 5% fetal calf serum (FCS)and 10 μg/ml insulin in 95% air, 5% CO₂ at 37° C. (Karey, K. P. et al.,1988, Cancer Res. 48:4083-4092.) Cells are transferred every 4-6 daysand seeded at 1.75×10⁶ cells/plate in 20 ml medium in a 10 cm dish.

MCF-7 cells are cultured as described above. Six-week-old female nudemice (nu/nu, Sprague Dawley, Madison, Wis.) are injected subcutaneouslyin the back with 5×10⁶ MCF-7 cells in 0.05 ml serum-free medium.Estrogen production in the mice is inadequate to support growth ofMCF-7, so the mice are given injections of beta-estradiol dissolved insesame oil (0.1 mg/0.05 ml oil s.c.) beginning one day before injectionof the cancer cells and weekly thereafter. Tumors are allowed to growuntil a diameter of 5 mm. (Hardman, W. E., et al., 1999, Anticancer Res.19:2269.)

When the tumors reach 5 mm, IGF-1, ¹³¹I-IGF-1, or ⁹⁰Y-IGF-1 is injectedat half its maximal tolerated dose in 5 mice each. Five control micereceive no agent.

Tumor size is monitored every 3 days.

Results:

It is determined that mice harboring MCF-7 tumors and receiving¹³¹I-IGF-1 or ⁹⁰Y-IGF-1 survive longer and have slower tumor growth thancontrol mice receiving no treatment or receiving unlabelled IGF-1.

Example 2 Treatment of a Mouse Breast Cancer Model with IGF-1-dgRicin Aconjugate Materials and Methods

Ricin A chain is prepared as described in Gregg, E. O. et al. (1987, J.Immunol. 138:4502-08). Ricin A chain is deglycosylated as described inBlakey, D. C. et al. (1987, Cancer Res. 47:947-952).

The conjugation procedure is generally as described in Thorpe, P. E. etal. (1982, Immunol. Rev. 62:119-158) and Huang, X. et al. (2004,Prostate 61:1-11). To a solution of IGF-1 (1 ml, 10 mg/ml) in 50 mMborate buffer (pH 9.0) was added 1.2 mg4-succinimidyloxycarbonyl-methyl-α-[2-pyridyldithio]toluene (SMPT,Pierce Biotechnology) dissolved in 10 μl dimethylformamide. That isapproximately a 3:1 molar ratio of SMPT to IGF-1. After 30 minutesstifling at room temperature, the reaction mixture is passed through aSephadex G-25 column equilibrated with 0.1 M sodium acetate, 0.1 M NaCl,pH 4.5. The derivatized protein is eluted with the same buffer.Deglycosylated ricin A chain is derivatized with SMPT by the sameprocedure at a ratio of 2.6 SMPT per ricin A chain molecule. Thederivatized deglycosylated ricin A is separated from reagents by passingthe solution through a SEPHADEX G-25 column equilibrated with 0.1 Msodium acetate, 0.1 M NaCl, pH 4.5.

The derivatized IGF-1 is concentrated to 2.5 ml, and 10 mg ofdithiothreitol is added. After stirring for 30 minutes at roomtemperature, the solution is passed through a SEPHADEX G-25 columnequilibrated with nitrogen-flushed PBS. The eluted IGF-1 is run directlyinto a solution of the derivatized deglycosylated ricin A to react in amixture with a 1:1.5 ratio of IGF-1 to deglycosylated ricin A (dgA). Thereaction forms an IGF-1-dgA conjugate with 1 dgA per IGF-1.

Conjugates with 1 dgA per IGF-1 are purified by size-exclusionchromatography on SUPERDEX 200. The conjugate is characterized bySDS-PAGE to verify that the material consists of purified conjugate with1 IGF-1 linked to 1 deglycosylated ricin A chain. The structure of theconjugate is shown below, where the linker is attached to lysine sidechains or the N-terminal alpha-amino groups of the proteins.

Mouse treatment: MCF-7 cells are cultured as described above.Six-week-old female nude mice (nu/nu, Sprague Dawley, Madison, Wis.) areinjected subcutaneously in the back with 5×10⁶ MCF-7 cells in 0.05 mlserum-free medium. Estrogen production in the mice is inadequate tosupport growth of MCF-7, so the mice are given injections ofbeta-estradiol dissolved in sesame oil (0.1 mg/0.05 ml oil s.c.)beginning one day before injection of the cancer cells and weeklythereafter. Tumors are allowed to grow until a diameter of 5 mm.(Hardman, W. E., et al., 1999, Anticancer Res. 19:2269.)

The maximal tolerated dose of the conjugate is determined by i.p.injection of a range of doses of the conjugate into mice. Then half themaximal tolerated dose of the conjugate is injected i.p. into 5 micewith 5 mm tumors. Five control mice with 5 mm tumors are untreated.Tumor size is monitored every 3 days thereafter.

Results:

It is determined that mice receiving the IGF-1-dgA conjugate survivelonger and have slower tumor growth than control untreated mice.

Example 3 Treatment of a Mouse Breast Cancer Model with DiphtheriaToxin-IGF-1 Fusion Protein Materials and Methods:

A fusion protein containing at its N-terminus residues 1-389 ofdiphtheria toxin followed by a variant form (SEQ ID NO:10) of IGF-1 thatdoes not bind to the soluble IGF binding proteins is synthesized. Thediphtheria toxin-IGF-1 fusion protein (DPT-IGF-)1 is SEQ ID NO:12. It isexpressed from a pET vector (G.E. Lifesciences) having the sequence ofSEQ ID NO:14.

E. coli transformed with the SEQ ID NO:14 plasmid are grown in LBmedium, with 50 μg/mlkanamycin at 37° C. At an O.D. 600 nm ofapproximately 0.4, 1 mM IPTG is added to stimulate expression ofDPT-IGF-1 from the T7 promoter. After 4 hours, the cells are harvested.Cells are broken, inclusion bodies are collected and washed, and thefusion protein is purified from inclusion bodies as described invanderSpek, J. C. et al., 2000, Meth. Enzymol. 327:239. The DPT-IGF-1fusion protein is refolded by dilution to 0.1 mg/ml in 2 M urea, 50 mMTris-HCl, 20 mM glycine, 1.5 mM EDTA, 0.4 mM dithiothreitol, pH 9.1 for2 hours at room temperature. The refolded protein is concentrated byultrafiltration.

The DPT-IGF-1 fusion protein is tested against MCF-7 breast cancer cellsin mice by i.p. or i.v. injection as described in Examples 1 and 2.

Results:

It is determined that mice receiving the DPT-IGF-1 fusion proteinsurvive longer and have slower tumor growth than control untreated mice.

Example 4 Treatment of a Mouse Breast Cancer Model with a Clostridiumperfringens Enterotoxin-IGF-1 Fusion Protein Materials and Methods:

A fusion protein containing residues 45-223 of Clostridium perfringensenteroxin fused to a variant form (SEQ ID NO:10) of IGF-1 that does notbind to the soluble IGF-1 binding proteins is synthesized. ThisCPE-IGF-1 fusion protein is SEQ ID NO:11. In addition to the CPE moietyand the IGF-1 moiety, the fusion protein also contains at its N-terminusmethionine followed by 6 His residues as a purification tag, followed byan enterokinase cleavage recognition sequence at residues 8-13. CPEresidues 45-223 begin at residue 14 of the fusion protein. The variantIGF-1 moiety follows the CPE segment at the C terminal, beginning atresidue 193 of the fusion protein. The fusion protein is encoded andexpressed from a plasmid derived from a pET vector (GE Lifesciences).The plasmid sequence is SEQ ID NO:13.

E. coli transformed with the SEQ ID NO:13 plasmid are grown in LBmedium, with 50 μg/mlkanamycin at 37° C. At an O.D. 600 nm ofapproximately 0.4, 1 mM IPTG is added to stimulate expression ofDPT-IGF-1 from the T7 promoter. After 4 hours, the cells are harvested.Cells are broken as described in vanderSpek, J. C. et al., 2000, Meth.Enzymol. 327:239. The CPE-IGF-1 fusion protein is purified from thesoluble fraction by passing the soluble fraction through a 10 ml packedcolumn of HIS-SELECT nickel chelate affinity column (Sigma, St. Louis,Mo.). The CPE-IGF-1 fusion protein is eluted with 25 mM Tris, 250 mMimidazole, pH 8.0. The CPE-IGF-1 fusion protein is also purified frominclusion bodies as described in Example 3.

The CPE-IGF-1 fusion protein is tested against MCF-7 breast cancer cellsin mice by i.v. or i.p. injection as described in Examples 1 and 2.

Results:

It is determined that mice receiving the DPT-IGF-1 fusion proteinsurvive longer and have slower tumor growth than control untreated mice.

All cited patents, patent documents, and other references areincorporated by reference.

1. An insulin-like growth factor-1 (IGF-1) receptor ligand carrying atherapeutic radionuclide; wherein the ligand is an IGF-1 receptoragonist.
 2. The IGF-1 receptor ligand of claim 1 wherein the ligand iscoupled to the radionuclide by a linker moiety.
 3. The IGF-1 receptorligand of claim 1 wherein the linker moiety comprises a chelator.
 4. TheIGF-1 receptor ligand of claim 1 wherein the therapeutic radionuclide isIodine-131, Yttrium-90, Indium-111, Rhenium-186, or Lutetium-177.
 5. TheIGF-1 receptor ligand of claim 1 wherein the ligand is a variant IGF-1protein that has reduced binding affinity for the soluble IGF-1 bindingproteins.
 6. The IGF-1 receptor ligand of claim 5 wherein the ligandcomprises SEQ ID NO:10.
 7. The IGF-1 receptor ligand of claim 5 whereinthe ligand is IGF-1.
 8. The IGF-1 receptor ligand of claim 1 wherein theligand has a greater affinity for the IGF-1 receptor than for theinsulin receptor. 9-20. (canceled)